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# Help with Polar coordinates

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I need to know how to find the polar coordinates of (21, 48); I figured out r (52.4) but I can't figure out the theta even after so many instructional videos! I have the answer (Theta is 66.4) but I can't figure out how to get to it!

Guest May 10, 2017
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I forgot to mention that the original coordinates are rectangular, sorry!

Guest May 10, 2017
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I may not be able to explain any better...but I will try!

Here is just a graph of the point (21, 48).

Theta is the angle that a line from the origin to the point makes with the positive x-axis.

The second one is the same graph, just with some more markings on it.

Look at the second picture. This is just a right triangle! And...in every right triangle,

So..

tan θ = 48/21

θ = atan(48/21)

θ ≈ 66.371º

And we can use the Pythagorean theorem to find the hypotenuse...which is r.

212 + 482 = r2

r = $$\sqrt{441+2304}\approx52.393$$ ...just as you found!

hectictar  May 10, 2017
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Thank you soooo much, this definitely helped!

Guest May 11, 2017